1. Field
This invention is in the field of devices for monitoring specific gravity of a solution, and is particularly concerned with monitoring continuously electronically.
2. State of the Art
Float type hydrometers have been used for many years to measure the specific gravity of a solution. These, however, do not lend themselves to continuous, remote monitoring of the solution. It is known that solutions containing ions will support a current flow and that the resistance to current flow between two electrodes immersed in such a solution is a function of the specific gravity of the solution. Thus, by measuring the resistance of the solution, an indication of the specific gravity of the solution can be obtained. Various circuits utilizing conductivity probes have been suggested. However, those that utilize a D.C. voltage across the electrodes in the probe generate considerable gas at the surface of one or both of the probes, which interferes with accuracy of measurement. Further, such probes have generally been directly connected to a meter that indicates current flow through the solution being measured. Since the current changes that take place with changes in specific gravity are usually very small and difficult to detect directly with a meter, accuracy is lacking in such systems. Systems applying A.C. voltage across a conductivity cell have been suggested, but have used complicated arrangements for the substitution of series and shunt resistances so that voltage across the conductivity cell varies in accordance with the logarithm of the conductivity measured by the cell. These prior systems all leave much to be desired.
3. Objective
It was a principal objective of the invention to provide a simple and easy to use and maintain electronic system for measuring variations in specific gravity of a solution.